Why transformer is rated in kva

kVA is the unit for apparent power. Apparent power consists of active and reactive power. Active power is the share of the apparent power which transmits energy from the source (generator) to the user. Reactive power is the share of the apparent power which represents a useless oscillation of energy from the source to the user and back again. It occurs when on account of some »inertia« in the system there is a phase shift between voltage and current. This means that the current does not change polarity synchronous with the voltage. But the heat generated in a winding as well as the eddy current losses generated in a transformer core depend on the current only, regardless of whether it aligns with the voltage or not. Therefore the heat is always proportional to the square of the current amplitude, irrespective of the phase angle (the shift between voltage and current). So a transformer has to be rated (and selected) by apparent power. It is often helpful to think of an extreme example: Imagine a use case where the only and exclusive load is a static var compensator (and such cases do exist). Would the load then be zero because the active power is zero? Most certainly not. – Caution: In this situation the voltage across the output terminals will increase with load rather than drop! Supplement: Special care has to be taken if the load current of a transformer includes any higher frequencies such as harmonics. Then the transformer may even overheat although the TRMS load curre...

balaji Generator is producer of Voltage and Current, we can connect load as such draining full load current or half load, even noload,but voltage remain moreover same.So it willl rated in terms of product of V*I, secondly it gives a electrical output for any Load(may Capacitor,Inductor & resistor),so it is consider as Procuct of Voltage & Current excluding powerfactor. Whereas motor is machines coverts electrical Energy to Mechanical energy, so it is rated in KW zulfiquar wani Generator and transformer are rated in KVA becoz at that time we dont know the consumer power factor as we know that the (KW= KVA X Cos Phi) as we know the power factor we have ratings in KW and on the other hand motor has defined power factor and the rating has been mentioned in KW for example if we have transformer of rating 50KVA this rating of transformer is its apparent power that is KVA if we multiply the same withh the power factor 0.85 we will get the real power that is KW KW= KVA X Cos phi KW = 50 X 0.85 KW= 42.5KW p tiwari Generator is a source of power. It includes active as well as reactive power. It deliver only active power while working on unity power factor. It deliver reactive power only while connected to a purely reactive load. It can deliver both of these powers while connected to a composite load. This signifies that the current limit is the main factor here. You can draw a purely rective current of rated value or purly active current of rate value. combination of output depends ...

What is a Transformer Rating? Manufacturers design transformers based on the voltage and current required for the transformer’s operation. They then specify this on the transformer’s nameplate in terms of VA (Volt-Amps). This is referred to as the rating of a transformer. The transformers rating can also be the maximum voltage and current that can be safely applied to the transformer. The rating of a transformer depends upon temperature rise, which depends on the transformer’s losses. However, the temperature can be maintained within permissible limits by using the proper cooling system. The greater the effectiveness of the cooling system, the higher the rating of the transformer (and vice versa). For a given cooling system, the rating of an electrical machine is indirectly determined by the losses present in the machine. In a transformer, there are two main types of losses: • Constant losses or core losses – These depend on V • Variable losses or ohmic (I 2R) losses – These depend on I Hence total losses depend on V and I. Since the rating of a transformer depends upon losses and losses depends upon V and I, the rating of a transformer depends on V×I, which is also termed VI ratings. As losses are independent of the That’s why the Lets us take an example, a transformer working on rated voltage and rated current with load power factor equal to zero; as load power factor is zero, it will deliver zero power to load, but it has rated kVA output. Hence rating must be expressed...

A generator is rated in KW at a certain power factor so it too is rated in kVA. A generator is converting mechanical energy from the prime mover to electrical energy.The engine, turbine, windmill, waterwheel, or kid on a bicycle spins the generator is rated in horsepower = kW.The generator cannot produce any more kw than is supplied by the prime mover.That given, specifying its size in kW makes sense. A transformer can handle its rated kVA at any power factor.A 100 kVA generator, rated at 0.8 pf = 80 kW cannot supply more than 80 kW.A 100 kva transformer can deliver 100 kw at 1.0 power factor. RE: Why are generators rated in kW and transformers in kVA (Electrical) Generator is power generator (coverts the form of energy) and its ability to deliver the real power is limited by its prime movers capacity in kW or HP. Where as the reactive power that makes up total KVA can be almost anything by sizing the alternator accordingly. The kVA rating is limited by the alternator. So it has both ratings, kW and kVA and neither should be exceeded. The transformer is only a pressure (voltage) changer and does not care whether power passing through itself is reactive or resistive or its combination. Its ability is limited only by amperes it can pass through at a given voltage, hence only kVA rating matters. Most kW it can pass thorough would be equal to its kVA rating at unity power factor. Rafiq Bulsara RE: Why are generators rated in kW and transformers in kVA (Electrical) 29 Sep 09 22...

Any piece of electrical equipment is rated based on how much current it can handle at a particular voltage and the losses occurring in it. The same applies to power transformers also. Transformers are rated based on the maximum power that they can transfer from their primary side to the secondary side while taking losses into account and are rated in VA, kVA, or MVA and never in KW. KVA stands for kilo-volt-ampere, which basically is the unit of electric power. While calculating the kVA of any piece of equipment the power factor is not taken into account. (i.e.) Power in kVA = Voltage x Current. This means kVA is the unit of measurement for that equipment in which the output power is independent of the power factor. For example Rating of Alternators, Transformers, UPS, etc. On the other hand, KW (KiloWatts) is also the unit of electric power for that equipment in which the power factor plays a role. Normally machines that produce a mechanical output are rated in kilowatts. For example the rating of electric motors. Read More about power factor. Why are transformers rated in KVA but not in KW? Transformers are energy transfer device that transfers power from the primary side to the secondary side without altering the energy level (considering zero power loss). Iron loss and copper loss occurring in the transformer are also independent of the power factor. Moreover, the output power factor of the transformer purely depends on the connected load. The transformer does not alte...

Electric transformer rating makes or breaks your electrical project. This is because under rating the transformer can cause it to fail, breakdown or completely damaged. It happened in my work, one of the most critical transformers had a serious damage, and we had to replace it ASAP to reconnect loads. • • • • • • • • • • • • • • • • • Standard KVA Rating of Transformers We use KVA for transformer rating, (KVA means Kilo volt Ampere). To determine the size of the transformer, it is important to determine the load by KVA. However, Transformers are mostly used for the purpose of power distribution, that’s why common standard KVA transformers are common to use. Two types of transformer KVA ratings are mentioned below. For three Phase Delta Wye transformer 408 to 120/208 common standard KVA ratings are 15 KVA, 30 KVA, 45 KVA, 75 KVA, 112.5 KVA, 225 KVA, 300 KVA, and 500 KVA. For a Single-phase transformer with the size of 277- or 480-Volt transformer common standards are 5 KVA, 7.5 KVA, 10 KVA, 15 KVA, 25 KVA, 37.5 KVA, 50 KVA, 75 KVA, and 100 KVA. Please note, Besides the mentioned standard ratings there are other sizes of transformer available. However, the most common size is mentioned above. Transformer KVA Rating Formula The transformer KVA rating formula is derived from the power rating of the transformer. In this article, we will include a formula for both single-phase and three-phase transformers. So, let’s start with the formula of single-phase Transformer. Single Phas...

kVA= 1000VA or volt-amps and kW= 1000 W or watts Many of us are frequently asked a question “why transformer and alternators are rated in KVA and not in KW?” In this article you can see the short and simple explanation to this question. So, let’s get started…. Transformer is an static electrical device that transfers the power from one circuit to another without changing the value of power and frequency. In other words, it can only step up or step down the value of current and voltage while the power and frequency would remain same. • Related Post: To explain the topic we need to know about the Types of losses in transformer. There aretwo types oflosses in a transformer: 1.Copper Losses 2.Iron Losses or Core Losses • Copper losses (I²R)depend on currentwhich passing through transformer winding whileIron losses or core losses orInsulation losses depend on Voltage. I.e. total losses depend on voltage (V) and current (I) which expressed inVolt ampere(VA) and not on the load power factor (p.f) [KW is Watts which is Volts V multiplied by Amps A multiplied by Power Factor( V x A x PF) .] That’s whythe transformer rating may be expressed in VA or kVA, not in W or kW. • Related Post: Another reason: First, we know anequation Watts =kVA*p.f When manufactures design a transformer, they have no idea which kind of load will be connected to the transformer. The load may be resistive (R), inductive (L), capacitive (C) or mixed load (R, L and C). Its mean, there would be different powerf...